The present invention relates to a method of and the apparatus for measuring the inside information of substance with the use of light scattering, in which light is irradiated from the surface of substance into the inside thereof and, after the light is diffused inside of the substance, the light is received at one point on the substance surface, thereby to measure variations of the light intensity according to the nature of the inside of the substance.
When the degree of oxygen saturation of the blood or the tissue of a predetermined part of a living body is measured, it is possible to know the reduction or oxidation condition of hemoglobin (Hb) of the blood in the tissue. Based on such a condition, the metabolism of the organ may be evaluated.
In this connection, there have been proposed a variety of methods of properly measuring the degree of oxygen saturation above-mentioned. Of these, public attention has been recently attracted to an optical method capable of executing such a measurement without injury of a living body. According to this optical measuring method, near-infrared rays less dangerous to a living body are irradiated to a living body and, after being diffused or scattered in the living body, the light is received to measure the composite light absorptivity by oxyhemoglobin (HbO.sub.2) and reduced hemoglobin (Hb) in the living body. According to this method, the component ratio of HbO.sub.2 to Hb may be acquired.
More specifically, the molecular absorption coefficients of HbO.sub.2 and Hb at each wavelength differ from each other. The composite molecular absorption coefficient of HbO.sub.2 and Hb of the living body at each wavelength is regarded as a value ranged between the molecular absorption coefficient of HbO.sub.2 and the molecular absorption coefficient of Hb. By measuring such a value, an approximate component ratio of HbO.sub.2 to Hb may be presumed. For example, when this value is in the vicinity of the molecular absorption coefficient of HbO.sub.2, it means that HbO.sub.2 is a dominant component. On the other hand, when this value is in the vicinity of the molecular absorption coefficient of Hb, it means that Hb is a dominant component.
However, this method cannot eliminate the influence of the total amount of hemoglobin exerted upon the molecular absorption coefficients. Accordingly, the isobestic point of light absorption spectra of HbO.sub.2 and Hb is used as a standard.
More specifically, the light absorption spectra of HbO.sub.2 and Hb present an isobestic point in the vicinity of 800 nm as shown in FIG. 12. In the area of wavelength longer than 800 nm, the molecular absorption coefficient of HbO.sub.2 is greater than the molecular absorption coefficient of Hb, while in the area of wavelength shorter than 800 nm, the molecular absorption coefficient of Hb is greater than the molecular absorption coefficient of HbO.sub.2. By measuring the molecular absorption coefficients at other wavelengths with the molecular absorption coefficients at the isobestic point serving as standards, the component ratio of HbO.sub.2 to Hb, i.e., the degree of oxygen saturation of blood may be acquired regardless of the amount of measured blood. There exist an equibestic pair and a contrabestic pair before and after the isobestic point. When the molecular absorption coefficients at these points are measured, the blood condition may be acquired with better precision (See Japanese Patent Publication No. 11614/1983).
According to a conventional measuring method, for example, as disclosed in the Publication above-mentioned, the end surfaces of two condensing fibers respectively come in contact with two points of the surface of a living body, and the reflected light or transmitted light of the light irradiated into the living body from one condensing fiber is received by the other condensing fiber. The light thus received is detected and converted, by a photosensor, into an electric signal, which is then subjected to a processing.
This method presents the following problems.
That is, it is difficult to cause the condensing fibers to accurately come in contact with a predetermined part of a living body at each measurement. As a matter of fact, the fiber contact points are always positionally shifted from the parts of a living body with which the fibers should come in contact. By such positional deviation, variations of the nature (such as the skin color, the amount of subcutaneous fat) peculiar to the measured part are disadvantageously entered. This deteriorates the reproducibility of the measurement results.